Critical care physicians frequently try to manipulate the preload of the heart to optimize cardiac function. There is, however, still debate as to what actually indicates the preload of the heart.
Although central venous pressure (CVP) is commonly used to estimate cardiac filling, it is often argued that it is a poor indicator of preload. This is likely true if one does not understand what preload is, principles of measurement with fluid filled systems, the effect of respiratory efforts on the measurement, the physiological determinants of CVP, and finally which point on the tracing to use as the estimate of the preload of the heart. When these are considered, however, the value of the CVP at the base of the ‘c’ wave gives a good indication of cardiac preload and a value which can be followed.
When properly measured CVP can be a useful guide to the filling status of the right ventricle. CVP is especially useful when followed over time and combined with a measurement of cardiac output. Importantly, preload is only one of the factors determining cardiac output and it must be integrated into a comprehensive approach that takes into account changes in cardiac function and the return of blood to the heart. Finally, the specific value of preload does not indicate volume responsiveness.
Department of Critical Care and Department of Physiology, McGill University Health Centre, Montreal, Quebec, Canada
Correspondence to Sheldon Magder, MD, McGill University Health Centre Rm D.03.6, 1001 Decarie Blvd, Montreal, QC, H4A 3J1, Canada. E-mail: firstname.lastname@example.org